Priority is claimed on Japanese Patent Application No. 2007-218295, filed on Aug. 24, 2007, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention is related to a magnetostrictive torque sensor.
2. Description of Related Art
Conventionally, there is known a magnetostrictive torque sensor, which detects a torque acted to the rotating shaft of a steering device of a vehicle, using a magnetostrictive film which has magnetic anisotropy and a coil (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2005-321316).
This magnetostrictive torque sensor repeatedly energizes and disconnects a detection coil by using a switching element, and maintains a voltage between the earths of the detection coils by a peak or trough hold circuit during energization, and detects the torque acted to the shaft based on an output signal of the hold circuit.
However, in the above conventional magnetostrictive torque sensor using the hold circuit, generally, there is a resistor or a capacitor between the earths on the input side so as to obtain a good detection characteristics by suppressing disturbances to an input signal. Therefore, there is a problem in which the level of detection voltage on the input side of the hold circuit goes down due to the resistor or the capacitor.
In addition, since the output side of the hold circuit becomes high impedance state in order to maintain detection sensitivity, the output signal is disadvantageously affected by disturbances such as a static electricity or a radio transmission.
The present invention was made in view of the above-mentioned circumstances and has an object of providing a magnetostrictive torque sensor which can suppress the effect of disturbances without reducing detection sensitivity.